Answer to Question #1005 Submitted to "Ask the Experts"

1. A radiation level of 10 Gy (1000 rad) delivered in a few minutes (acute exposure) would result in death in a very high percentage of cases (probably 90% or more) within 60 days of exposure (assuming no medical treatment). The underlying causes of death would be gastrointestinal injury coupled with bone marrow failure. If the dose exceeded 30 Gy (3000 rad) death might occur within a few days due primarily to central nervous system injury and cardiovascular collapse.
    
2. There would be a 50% chance of death within 60 days of exposure. If the patient survives the first two months there could be transient/permanent sterility. Other tissues (bone marrow, gut, etc.) might experience transient effects. There is also a significant increased risk of cancer that would likely appear years or decades after exposure.
    
3. 25 gigagrays would result in an instantaneous (within a few hours) death, assuming a whole-body exposure.

Kenneth L. Mossman, PhD Professor of Health Physics

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There is no unique number for an instantly lethal radiation dose; the best guess is 2,000-5,000 rad (20-50 Gy) and even then the death will not be instant as in breathing cyanide or CO. I asked my colleague, Dr. Heather Gepford, and she gave me the following additional information. Introduction to Radiobiology (A.H.W. Nias) states, "After a single dose of several thousand centigrays to the whole body, particularly the head, the clinical onset is prompt and death may occur in minutes to hours. After more than 50 Gy, there are seizures ranging from generalized muscle tremor to epileptoid convulsions similar to grand mal. This convulsive phase lasts a few hours and is followed by ataxia." The Biological Basis of Radiation Protection Practice (Editor, Kenneth L. Mossman) states, "At about 20 to 30 Gy and higher, the dysfunctions of the central nervous and cardiovascular systems are dramatic and irreversible. Also, there is a breakdown of the blood-brain barrier that leads to cerebral edema." Later in the same chapter it says that beginning around 20-30 Gy the neurovascular malfunctions result in coma and death within hours to a day or two. The Handbook of Health Physics and Radiological Health gives a range of 20-50 Gy for cardiovascular or toxemic acute radiation syndrome and 50 Gy for nervous system ARS. A hard number is difficult to come up with since every individual responds differently and we have (fortunately) had very few exposures sufficient to cause immediate death. I am trying to obtain some historical accident data for "real world" numbers. Question: What is the average radiation reading on nuclear waste? There is no single answer to this question. Obviously the radiation reading ( on the surface) depends on (a) what is in the waste, (b) how much of it, (c) what is the wall of the container. The reading on the surface of a radioactive package may range from as low as background to thousands of rad per hour.

Nicholas Tsoulfanidis, PhD